Recent years have seen vigorous development in fuel cell vehicles and the like. Concurrently, hoses for dispensing hydrogen to fuel cell vehicles and the like from a dispenser installed in a hydrogen station have also been developed. Such hydrogen-dispensing hoses require superior hydrogen gas permeation resistance. Because fuel tanks must be filled with hydrogen gas at high pressure in order to increase the travel distance of a fuel cell vehicle or the like, a hydrogen-dispensing hose must have practical utility capable of withstanding high levels of internal pressure of 70 MPa and greater. Strengthening reinforcing layers is a common method of improving the pressure resistance of a hose; however, if a metal reinforcing material is used as a constituent member of a reinforcing layer, there is the risk of the metal being made brittle by the hydrogen, thereby reducing the life of the hose. Thus, proposals have been made to form all reinforcing materials by braiding polyparaphenylene benzobisoxazole (PBO) fibers (see Japanese Unexamined Patent Application Publication Nos. 2010-31993 and 2011-158054).
A hose fitting including a nipple and a socket is attached to an end of the hose. Typically, to attach the hose fitting to the hose, an end of the hose is sandwiched between the nipple and the socket, and, in that state, the socket is crimped, i.e., deformed so as to decrease in diameter, by compressing the outer circumferential surface of the socket. Because a hydrogen-dispensing hose such as described above must have high pressure resistance, there must be a commensurate improvement in the leak resistance and seal integrity of the hose fitting, resulting in increased crimping force. Excessive crimping force will result in disruption of the braided structure of the reinforcing layers (especially the outermost reinforcing layer). In addition, as the pressure of the hydrogen flowing through the hose increases, the degree of dimensional change (increased diameter and axial contraction, or decreased diameter and axial elongation) in the hose will increase, thereby promoting disruption of the braided structure of the reinforcing layers in the section crimped by the hose fitting. Such disruption of the braided structure is a factor that reduces the pressure resistance and durability of the hose.
In addition, as hydrogen pressure increases, the inner surface layer is subjected to greater internal pressure, and is liable to exhibit dimensional change (diameter-expansive deformation, etc.). The inner surface layer contacting the hydrogen is subjected to low, below-freezing temperatures (for example, around −40° C.), causing the layer to become brittle, and thus liable to be damaged even by small dimensional changes. Thus, it is necessary to suppress dimensional changes in the hose in order to improve the pressure resistance and durability of the hose.
A hose provided with a fiber reinforced layer formed by braiding PBO fibers has superior pressure resistance and durability. However, in a hose in which the reinforcing layer is constituted only by a fiber reinforced layer of braided high-strength fibers of this sort, it is difficult to ensure sufficient pressure resistance and durability if the pressure of the flowing hydrogen is greater than normal. This also impedes suppression of dimensional changes in the inner surface layer. Thus, improvement is desired.